1. Field of the Invention
The present invention relates to a sensor array and a transmitting/receiving device, and more particularly, to a sensor array, such as an ultrasonic probe for use in an ultrasonic diagnostic device, an ultrasonic microscope, a metal flaw detector, and the like, and to a transmitting/receiving device.
2. Description of the Related Art
As the background of the present invention, an ultrasonic probe or the like used in a conventional ultrasonic diagnostic device is disclosed in, for example, xe2x80x9cHybrid Multi/Single Layer Array Transducers for Increased Signal-to-Noise Ratioxe2x80x9d, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 44, No. 2, March 1997.
FIG. 9 is a perspective view showing the principal part of an ultrasonic probe used in a conventional ultrasonic diagnostic device, and FIG. 10 is a perspective view of a piezoelectric vibrator used in the ultrasonic probe. An ultrasonic probe 1 shown in FIG. 9 includes a substrate 2 made of a sound-absorbing material called a xe2x80x9cpacking materialxe2x80x9d. A plurality of piezoelectric vibrators 3 are fixed in a matrix onto one principal surface of the substrate 2.
Each piezoelectric vibrator 3 includes a plurality of stacked piezoelectric layers 4, as shown in FIG. 10. Inner electrodes 5 are formed between the piezoelectric layers 4, and outer electrodes 6 are formed on the uppermost and lowermost surfaces of the piezoelectric layers 4. Via holes 7 are formed at both ends of the piezoelectric layers 4, and connecting electrodes 8 are formed in each of the via holes 7. The piezoelectric layers 4 are alternately polarized in opposite thickness directions. The piezoelectric vibrators 3 are bonded on one principal surface of the substrate 2 with an adhesive so that the principal surfaces of the piezoelectric layers 4 are placed in parallel therewith.
Furthermore, an acoustic matched layer 9 is formed on the piezoelectric vibrators 3 so as to establish an acoustic matching with the human body, and an acoustic lens 10 is formed on the acoustic matched layer 9 so as to converge the ultrasonic waves.
While the inner electrodes 5 are led out by the via holes 7 in the piezoelectric vibrators 3 used in the above-described ultrasonic probe 1, they may be led out from the side faces as in a general type of multilayer capacitor and the like.
Since the piezoelectric vibrators 3 used in the ultrasonic probe 1 shown in FIG. 9 do not have a single-layer structure, but have a multilayer structure, functions and resolution can be improved, and sensitivity is high. However, a high machining accuracy for the via holes and a high printing accuracy for the electrodes are required during production, and it is difficult to align the via holes due to the contraction of the material when being fired and to cut the fired material into a matrix. Moreover, the outer electrodes are prone to fall off after cutting. Accordingly, an extremely high machining accuracy is necessary during production, so there are many problems in production, and the characteristics are prone to vary.
When the inner electrodes 5 of the piezoelectric vibrators 3 in the ultrasonic probe 1 are led out from the side faces, a high machining accuracy is also necessary during production.
Accordingly, a highly sensitive ultrasonic probe, which is easily produced, has been invented, as in Japanese Patent Application No. 11-273078 of the present applicant. FIG. 11 is a perspective view showing the principal part of such an ultrasonic probe, and FIG. 12 is a perspective view of a piezoelectric vibrator used in the ultrasonic probe. An ultrasonic probe 1 shown in FIG. 11 is different from the ultrasonic probe 1 shown in FIG. 9 particularly in the piezoelectric vibrators 3. That is, while the piezoelectric layers 4 and the inner electrodes 5 are vertically stacked on one principal surface of the substrate 2 in the piezoelectric vibrators 3 of the ultrasonic probe 1 shown in FIG. 9, piezoelectric layers 4 and inner electrodes 5 are stacked in a direction parallel to the side faces of the piezoelectric vibrator 3 in the ultrasonic probe 1 shown in FIG. 11.
The ultrasonic probe shown in FIG. 11 is also highly sensitive because the piezoelectric vibrators having a layered structure are used.
The ultrasonic probe shown in FIG. 11 can be produced by making a laminated member by stacking a plurality of piezoelectric layers and a plurality of inner electrodes, cutting the laminated member in the stacking direction to form a plate like motherboard, forming outer electrodes on principal surfaces of the motherboard, fixing the motherboard on one principal surface of the substrate, and cutting the motherboard into a plurality of piezoelectric vibrators. Since the outer electrodes are formed on the entire principal surfaces of the motherboard, a high positioning accuracy is unnecessary when fixing the motherboard onto the substrate, and this facilitates production.
In the ultrasonic probe shown in FIG. 11, however, the thicknesses of the piezoelectric layers constituting the piezoelectric vibrators vary and cannot be fixed.
In order to produce piezoelectric vibrators of a fixed shape, it is necessary to decrease and adjust the thicknesses of the piezoelectric layers disposed on the sides of the piezoelectric vibrators. In this case, it is impossible to apply a voltage to the piezoelectric layers on the sides because they do not have any electrodes on their outer sides, and this is a component that damps vibration. The damping component has a great influence on the entire device, and is also the principal factor that decreases efficiency.
Moreover, since the thicknesses of the piezoelectric layers on the sides vary among the piezoelectric vibrators, the characteristics also significantly vary among the piezoelectric vibrators.
Accordingly, a main object of the present invention is to provide a highly sensitive sensor array which can be easily produced and in which variations in the characteristics among piezoelectric vibrators are limited.
Another object of the present invention is to provide a transmitting/receiving device including a highly sensitive sensor array which can be easily produced and in which variations in the characteristics among piezoelectric vibrators are limited.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a sensor array including a substrate, and a plurality of piezoelectric vibrators having a rectangular parallelepiped shape and fixed in a matrix on a principal surface of the substrate, wherein each of the piezoelectric vibrators includes a plurality of piezoelectric layers stacked in a direction parallel to the principal surface of the substrate, at least some of the piezoelectric layers being stacked in a direction crossing two adjacent side faces of the piezoelectric vibrator, inner electrodes disposed between the piezoelectric layers, and outer electrodes provided on end faces of the piezoelectric layers.
Preferably, the piezoelectric layers are stacked in a direction crossing two adjacent side faces of the piezoelectric vibrator at approximately 45xc2x0.
According to another aspect of the present invention, there is provided a transmitting/receiving device including the above sensor array.
The sensor array of the present invention is highly sensitive because the piezoelectric vibrators having a layered structure are used.
The sensor array can be produced by making a laminated member by stacking a plurality of piezoelectric layers and a plurality of inner electrodes, cutting the laminated member in the stacking direction to form a platelike motherboard, forming outer electrodes on principal surfaces of the motherboard, and fixing the motherboard on one principal surface of the substrate. Since the outer electrodes are formed on the entire principal surfaces of the motherboard, a high positioning accuracy is unnecessary when fixing the motherboard onto the substrate, and this facilitates production.
Since at least some of the piezoelectric layers and the inner electrodes are stacked in parallel with the principal surfaces of the substrate and in a direction crossing two adjoining side faces of the piezoelectric vibrators, the area of the end faces of the outermost piezoelectric layers in the piezoelectric vibrators, which do not show piezoelectricity, is reduced. For this reason, the factor that damps vibration in the outermost piezoelectric layers of the piezoelectric vibrators is reduced, and the influence of the variations in thickness among the outermost piezoelectric layers of the piezoelectric vibrators on the characteristics of the piezoelectric vibrators is lessened. Therefore, variations in the characteristics among the piezoelectric vibrators are limited.
The above objects, further objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention with reference to the drawings.